The invention relates to pneumatic tires and more particularly to a run flat pneumatic tire containing a thin annular band element which acts as a structural compression member when the tire is in the unpressurized or uninflated state which allows loads to act over a substantial portion of the circumference of the tire to enable the tire to run in the unpressurized condition, wherein the band element is comprised of multiple regions with an interior region being more elastic than radial outer regions providing high interlaminar shear strength to the band element.
Various tire constructions have been developed over the years which enable a tire to run in an uninflated or underinflated condition, such as after receiving a puncture and a complete or partial loss of pressurized air, for extended periods of time and at relatively high speeds. This enables the vehicle operator to safely drive the vehicle to an appropriate location for repair or replacement of the tire. These tires are referred to as xe2x80x9crun flat tiresxe2x80x9d and have been successful for certain applications and in certain types of tire constructions. One such type of run flat tire incorporates a thin annular high strength band element which acts as a tension member when the tire is pressurized and acts as a structural compression member when the tire is in the unpressurized or partially pressurized state, and are referred to as xe2x80x9cbanded run flat tiresxe2x80x9d. Some examples of such banded run flat tires are shown in U.S. Pat. Nos. 4,428,411; 4,673,014; 4,794,966; 4,456,084; 4,111,249; 4,318,434; 4,459,167; 4,734,144 and 5,879,484.
Most of the band elements used in these prior art run flat tires have predominantly been made of homogenous materials extending from a radially inside surface to a radially outside surface and form at least one solid thin annular band rigid enough to act as the structural compression member when the tire is in the unpressurized state. Other prior art run flat bands achieve a dual band stiffness by using prestressed fibers in order to improve band performance. Several embodiments of such prior art dual modulus band elements are shown in U.S. Pat. No. 4,456,084. One embodiment has greater resistance to bending forces which tends to decrease its local radius of curvature than to those tending to flatten it. Thus, the band element stiffness is lower for inflated conditions and provides good riding comfort but has a high stiffness in the uninflated condition. A second embodiment shown in this patent has a bending stiffness that increases with increasing stress irrespective of the bending direction. A third embodiment has a two step modulus in which deflection is resisted at one rate and final deflection is resisted at a higher rate. However, all of the dual modulus band elements of U.S. Pat. No. 4,456,084 have the characteristic of the bending stiffness changing as a result of deflection.
The common problem that exists with known prior art band elements which provide good ride characteristics in both the inflated and uninflated conditions is that they are susceptible to interlaminar shear stress and fracture which occurs along the neutral axis of the band. This fracture is due to the constant change in band axial geometry from circular-to-flat as the band moves through the central footprint region. This causes the fibers along the inside diameter of the band element to be in tension and elongate, while the fibers along the outside diameter of the band element are in compression and are shortened. In the uninflated condition, the sidewalls undergo significantly more deflection and thus the band element in the central footprint region conforms to the road surface for a longer distance on both sides of the center of the tire causing greater compression and tension on the band as it moves through the central footprint region. These problems are set forth more fully in U.S. Pat. No. 5,879,484, the contents of which are incorporated herein by reference.
Likewise, as the band element flattens in the central footprint region, there is a natural shearing effect within the band element in order for the inside diameter band element fibers to elongate while the outside diameter band element fibers are shortened. Thus, regardless of whether the band element is made of a homogenous filament wound material or a multi-layered tape fiber/resin composite, the strain/stress regime and transfer shear develop to some degree upon flattening of the band element in the central footprint region because the outer fiber stresses are proportional to the strains. This interlaminar shear strength controls the banded tire durability in both inflated and uninflated conditions.
In view of the problems set forth above, the need exists for an improved band element for placement in a run flat tire which is less susceptible to failure due to interlaminar shear than heretofore known prior art band elements.
The present invention provides a band element for a run flat tire which is formed of fiber and resin composites having three relatively distinct regions, wherein radially inner and outer regions are of a high modulus material and a central region near the neutral axis of the band, is of a material which is more elastic than the inner and outer regions thereby having a higher interlaminar shear strength than the inner and outer regions.
The invention provides increased interlaminar shear strength across the entire axial length of those band elements which heretofore only had increased strength at the axial ends achieved by tapering the ends thereof, thereby improving band element durability.
Still another aspect of the invention includes providing a band element having a unique arrangement of materials and fiber orientation which provides for optimum performance of the band element.
Another feature of the invention is to provide a band element wherein the central region is made of single or multiple layers of resin, either containing reinforcing fibers or being void of such fibers, with the outer and inner regions preferably being similar and formed of various types of high modulus resinous materials.
A further feature of the invention is to provide a band element wherein the central region is formed of rubber either containing reinforcing fibers or being void of such fibers.
Another aspect of the invention is forming the inner and outer regions of graphite reinforced resins and the interior region formed of a glass reinforced resin.
A still further feature of the invention is forming the central region of a wound fiberglass tow reinforced with fibers, which fibers are either randomly oriented, extend in the circumferential direction, or are spirally wound in the circumferential direction, with the inner and outer regions being filament wound layers of graphite reinforced resin.
A further aspect of the invention is to provide such a band element in which the inner and outer regions are reinforced with graphite fibers which extend predominantly in the circumferential direction, in combination with glass fiber reinforcement extending predominantly in the axial direction, and in which glass fibers are placed near the axial ends of the band in both the inner and outer regions.
Another feature of the invention is to provide a band element in which the inner, outer and central regions can be constructed by known fabrication techniques i.e., homogenous filament winding, non-homogeneous filament winding, multi-layer tape composite winding, winding with prepreg materials, winding with wet woven materials, winding with mats, winding with resin transfer molding processes, winding with wet or prepreg woven preforms, and various combinations of such fabrication techniques.
The foregoing advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings.